Drive partition labels: why/how do they change, and why are there extra in /dev?

I'm ashamed to even be asking this, but I have to no matter how goofy it is.

I have a server with 8 SDDs in it. I installed CentOS 6.2 using Kickstart. The idea was to only format the first 2 disks and leave the rest as jbod (software requirement). Initially it failed with a "KeyError: /dev/sda" message during drive partitioning, and a colleague of mine suggested I change the bootloader line from "--driveorder=sda,sdb,sdc,etc." to start at sdc. I did, and the installation succeeded.

Now that I'm logged in when I do fdisk -l I see that sda and sdb were actually created and partitioned according to my scheme, so in effect I have sda1 and 2, and sdb1 and 2. The rest of the drives are untouched as I'd wanted. Why did I have to specify a starting point of sdc to successfully install? Why doesn't the partition table start at sdc then; why did it revert to sda?

Also, when I do fdisk -l I notice that the partitions run like this: sda, sdb, sdc, sdd, sde, sdf, sdi, sdj. If I look in /proc/partitions this matches as well. /dev directory and /sys/block have sdg and sdh as well though. Why did the installation skip those two and go to "i"? Are they actually being used for something else? How can I tell?

Thanks.

transient

10-24-2012 07:59 PM

To add, I went ahead and ran two scripts that I would be using for deploying these servers. The first checks for the presence of an OS on the drives to make sure I didn't inadvertently screw with the wrong ones. It returned:

This makes me think there must be something actually there, but I don't know what and I'm concerned about continuing this with the remaining servers since I'm not sure what I'm affecting.

transient

10-24-2012 08:21 PM

And to further complicate things...upon reboot /dev/md0, which was using /dev/sda and /dev/sdb, is now using /dev/sda and /dev/sde. Fdisk -l shows sda and sde as the two formatted and partitioned drives as well. Should I now be moving this from the newb forum?

transient

10-26-2012 02:49 PM

I found (I think) that the order in which Linux detects drives during boot determines what labels it uses for each drive, which is why the drive I installed the OS on may be /dev/sda during one session and /dev/sde on another. I'm opening a separate thread to discuss the hdparm output.

syg00

10-26-2012 03:08 PM

Have a read of this for info on your disk naming issues - and how to avoid it.
Can't help with your other thread.